title: Control of polymerization shrinkage and stress in nanogel-modified monomer and composite materials.
abstract: OBJECTIVE
  This study demonstrates the effects of nano-scale prepolymer particles as additives to model dental monomer and composite formulations.
  
  
  METHODS
  Discrete nanogel particles were prepared by solution photopolymerization of isobornyl methacrylate and urethane dimethacrylate in the presence of a chain transfer agent, which also provided a means to attach reactive groups to the prepolymer. Nanogel was added to triethylene glycol dimethacrylate (TEGDMA) in increments between 5 and 40 wt% with resin viscosity, reaction kinetics, shrinkage, mechanical properties, stress and optical properties evaluated. Maximum loading of barium glass filler was determined as a function of nanogel content and composites with varied nanogel content but uniform filler loading were compared in terms of consistency, conversion, shrinkage and mechanical properties.
  
  
  RESULTS
  High conversion, high molecular weight internally crosslinked and cyclized nanogel prepolymer was efficiently prepared and redispersed into TEGDMA with an exponential rise in viscosity accompanying nanogel content. Nanogel addition at any level produced no deleterious effects on reaction kinetics, conversion or mechanical properties, as long as reactive nanogels were used. A reduction in polymerization shrinkage and stress was achieved in proportion to nanogel content. Even at high nanogel concentrations, the maximum loading of glass filler was only marginally reduced relative to the control and high strength composite materials with low shrinkage were obtained.
  
  
  CONCLUSIONS
  The use of reactive nanogels offers a versatile platform from which resin and composite handling properties can be adjusted while the polymerization shrinkage and stress development that challenge the adhesive bonding of dental restoratives are controllably reduced.
authors.affiliation: School of Dentistry, Federal University of Pelotas, RS, Brazil.
authors.forename: Rafael R
authors.initials: RR
authors.lastname: Moraes
authors.forename: Jeffrey W
authors.initials: JW
authors.lastname: Garcia
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Barros
authors.forename: Steven H
authors.initials: SH
authors.lastname: Lewis
authors.forename: Carmem S
authors.initials: CS
authors.lastname: Pfeifer
authors.forename: JianCheng
authors.initials: J
authors.lastname: Liu
authors.forename: Jeffrey W
authors.initials: JW
authors.lastname: Stansbury
mesh_terms: D017609:Barium Compounds / Q000737:chemistry; D003188:Composite Resins / Q000737:chemistry*; D003764:Dental Materials / Q000737:chemistry*; D055119:Elastic Modulus; D005782:Gels; D006801:Humans; D007700:Kinetics; D008027:Light; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry; D008768:Methylmethacrylates / Q000737:chemistry*; D008970:Molecular Weight; D053758:Nanoparticles / Q000737:chemistry*; D018583:Pliability; D011092:Polyethylene Glycols / Q000737:chemistry; D058105:Polymerization; D011109:Polymethacrylic Acids / Q000737:chemistry; D011140:Polyurethanes / Q000737:chemistry; D012031:Refractometry; D012821:Silanes / Q000737:chemistry; D012822:Silicon Dioxide / Q000737:chemistry; D012826:Silicone Elastomers / Q000737:chemistry; D019265:Spectroscopy, Near-Infrared; D013314:Stress, Mechanical; D013499:Surface Properties; D014783:Viscosity
chemical_list: D017609:Barium Compounds; D003188:Composite Resins; D003764:Dental Materials; D005782:Gels; D008689:Methacrylates; D008768:Methylmethacrylates; D011109:Polymethacrylic Acids; D011140:Polyurethanes; D012821:Silanes; D012826:Silicone Elastomers; C102738:barium glass filler; C029824:urethane dimethacrylate luting resin; C020946:triethylene glycol dimethacrylate; C017492:methacryloxypropyltrimethoxysilane; D011092:Polyethylene Glycols; D012822:Silicon Dioxide